The aims of the research are to study the host-parasite relationship of the leishmania-macrophage system, and to conduct biochemical studies on the vertebrate, amastigote form of the organism. To this end the following specific aims are listed: (1) To determine the course of Leishmania donovani infection in peritoneal macrophages of C57B1/6J mice cultivated in vitro. Evaluation of parasite killing after macrophage activation and correlation with recognized characteristics of activated macrophages will also be studied. (2) To investigate mechanisms of amastigote killing by activated macrophages and attempt to determine how the parasite survives in the phagolysosome of the macrophage before activation. (3) To establish some general physiological and biochemical characteristics of the leishmania amastigote. (4) To conduct a study on the biochemistry of the amastigote which will emphasize whether these forms utilize the principal pathways of carbohydrate metabolism. (5) To examine aspects of amastigote membrane function. Transport of sugars, amino acids and peptides will be evaluated. We will also ascertain if the amastigote membrane is intact or "leaky".